This invention relates generally to photo responsive materials and methods for their use. More specifically, the invention relates to a direct write imaging medium which is capable of having an image formed directly thereupon by a beam of light, without the use of any photo mask or negative.
Photolithographic and/or photo etch techniques are widely used in the fabrication of printed circuit boards, semiconductor devices, the preparation of printing plates, graphic arts, and a number of other such processes. Such photo techniques generally employ one or more masks, also referred to as photo tools. The photo tool is used as a master in the exposure of other photosensitive materials. In general, materials used for photo tools should have very high resolution and should be capable of presenting a high contrast, stable image at imaging wavelengths. That is to say, the photo tool material should have an image area which is highly absorbing of imaging wavelengths, and a background area which is highly transparent at imaging wavelengths. In addition, such photo tool material should exhibit relatively high resolution. Furthermore, such material should be easy to use, and should most preferably employ a dry imaging process which is free from toxic compounds.
In response to the foregoing needs, the art has investigated a number of ablation imaging systems. In such ablation systems, a high intensity flux of light energy is applied to an imaging material which contains a species which absorbs that energy. The absorption of light promotes localized heating which causes portions of the imaging material to be removed from a base substrate thereby creating an imagewise pattern corresponding to the illumination. In some instances, layers of metal are employed as in the manufacture of such films. Metals are highly efficient at absorbing incident illumination; however, many metals require fairly high levels of illumination to cause their ablation. In addition, metals have a very broad band of optical absorption; and in some instances, this is advantageous since the resultant films have a very high optical density throughout the visible and ultraviolet spectrum. However, in graphic arts, electronics and other specialized applications, ultimate use of photo masks and tools thus generated takes place at ultraviolet and near ultraviolet wavelengths, and the industry favors photo masks having reasonably good transparency at visible wavelengths, since this allows for ease of mask alignment.
In other instances, carbon, typically in the form of a fine dispersion of carbon black particles, is employed as light absorbing material in photo ablatable films. While carbon has very good light absorption characteristics in the infrared and near infrared portions of the spectrum, dispersions of carbon particles are relatively poor at absorbing shorter wavelengths of light, particularly light in the blue and infrared portion of the spectrum. As a result, compositions which employ carbon as an absorbing medium need to be very heavily loaded if the resultant products are to have reasonably good light absorption in the ultraviolet and near ultraviolet portions of the spectrum. Such heavily loaded films are very opaque at visible wavelengths; furthermore, it has been found that the presence of relatively large amounts of carbon actually decrease the sensitivity of such film since relatively large amounts of energy are required to ablate away the heavy carbon loadings.
In view of the foregoing, the inventors hereof have recognized that there is a need for an ablatable film which is relatively sensitive at infrared and near infrared wavelengths and which produces a photo generated image which has very high optical density at near ultraviolet and ultraviolet wavelengths. Furthermore, such film should most preferably be relatively transparent at visible wavelengths. As will be explained in greater detail hereinbelow, the present invention provides a photo ablatable film which may be used as a discrete photo tool, or in combination with other imaging layers. The material of the present invention has very high absorption at ultraviolet wavelengths, but can be fabricated to be relatively transparent at visible wavelengths. Furthermore, the material is low in cost and easy to use. These and other advantages of the invention will be apparent from the drawings, discussion and description which follow.
There is disclosed herein a light ablatable, ultraviolet absorbing imaging medium. The imaging medium includes a substrate member, which is most preferably a transparent substrate. A body of light ablatable, ultraviolet absorbing material is supported upon the substrate. The body includes a polymeric matrix having a carbon pigment dispersed in at least a portion of the thickness of the matrix. The matrix further includes an ultraviolet absorbing dye dissolved in at least a portion of the thickness of the matrix. Most preferably, the concentration of carbon in the body is selected to be such that the optical absorption of the body at a wavelength of 360 nm attributable to the carbon is less than 50% of the optical absorption of the body at 360 nm which is attributable to the remainder of the components thereof.
In some embodiments, the body of light ablatable material is configured as a single layer of said polymeric matrix wherein the carbon is dispersed therein and the dye is dissolved therein. In other instances, the body comprises a plurality of superposed layers including a first layer, which is closest to the substrate and which includes the carbon pigment therein but which does not include the dye. In this embodiment, a second layer, which is separated from the substrate by the first layer, has the dye dissolved therein. In one specific version of this embodiment, the first layer is devoid of any urethane polymer.
In specific embodiments, the dye comprises an azo dye having high absorption for ultraviolet and near ultraviolet wavelengths, and low absorption for visible wavelengths.
In a specific class of embodiments of this invention, a layer of photo responsive material, such as a photo polymerizable material or a photo degradable material, is disposed between the substrate and the body of light ablatable, ultraviolet absorbing material. In this embodiment, patterning of the light ablatable, ultraviolet absorbing material provides an integral photo mask atop the layer of photo responsive material, and this mask can be used in connection with the further photo imaging of the photo responsive material. Also disclosed herein are methods for using the materials of the present invention.